1. Field of the Invention
The present invention relates to a biometric authentication system which uses an IC card for identifying a subject person through biometric authentication.
2. Description of the Related Art
Information which only a subject person knows, such as a personal identification number and a password, is generally used as a means for identifying the subject person who conducts monetary transaction or whose room entrance or exit is checked, by using information apparatus such as computers. However, the personal identification number and password have a disadvantage of ease of identity theft if these are stolen by a third party. To overcome this disadvantage, attention has recently been paid to biometric authentication using biometric information such as fingerprints and irises which information is difficult for the third party to steal and is different for each individual.
As an individual identification method using biometric authentication, the following method is known being disclosed in JP-A-2001-344213. Biometric information of a subject person is stored beforehand in an IC card (biometric information stored in an IC card is hereinafter called “registration data”). When the subject person is to be identified, biometric information acquired with a biometric information sensor is input to the IC card (this information is hereinafter called “collation information”). The IC card executes a collation process for the registration data and collation data to thereby confirm whether the subject person is a real person. A binary judgement of whether the registration data and collation data are perfectly coincident or not cannot be made by biometric authentication. Therefore, judgement is made by calculating a similarity degree and an inconsistency degree between the registration data and collation data by using a specific algorithm, and comparing the calculation result with a preset reference value (threshold value). FIG. 18 shows an example of an inconsistency degree distribution for the registration data and collation data. In FIG. 18, the abscissa represents an inconsistency degree of collation, and the ordinate represents an occurrence frequency. An occurrence frequency curve 901 shows collation between registration data and collation data of a subject person, and an occurrence frequency curve 902 shows collation between registration data of the subject person and collation data of a third party. Normally, the curve 901 positions to the left of the curve 902 (has a smaller inconsistency degree). A biometric authentication threshold value 903 is set between the curves. If the inconsistency degree is smaller than the biometric authentication threshold value, it is judged that the subject person is a real person, whereas if the inconsistency degree is larger than the biometric authentication threshold value, it is judged that the subject person is a pretended person.